ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-27-1321-2009 Pre-storm <I>Nm</I>F2 enhancements at middle latitudes: delusion or reality? Mikhailov A. V. 1 Perrone L. 2 Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Troitsk, Moscow Region 142190, Russia Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Rome 00143, Italy 18 03 2009 27 3 1321 1330 Copyright: © 2009 A. V. Mikhailov 2009 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/27/1321/2009/angeo-27-1321-2009.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/27/1321/2009/angeo-27-1321-2009.pdf

A critical analysis of recent publications devoted to the <I>Nm</I>F2 pre-storm enhancements is performed. There are no convincing arguments that the observed cases of <I>Nm</I>F2 enhancements at middle and sub-auroral latitudes bear a relation to the following magnetic storms. In all cases considered the <I>Nm</I>F2 pre-storm enhancements were due to previous geomagnetic storms, moderate auroral activity or they presented the class of positive quiet time events (Q-disturbances). Therefore, it is possible to conclude that there is no such an effect as the pre-storm <I>Nm</I>F2 enhancement as a phenomenon inalienably related to the following magnetic storm. The observed nighttime <I>Nm</I>F2 enhancements at sub-auroral latitudes may result from plasma transfer from the plasma ring area by meridional thermospheric wind. Enhanced plasmaspheric fluxes into the nighttime F2-region resulted from westward substorm-associated electric fields is another possible source of nighttime <I>Nm</I>F2 enhancements. Daytime positive Q-disturbances occurring under very low geomagnetic activity level may be related to the dayside cusp activity.

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